[Mesa-dev] Moving amdgpu/addrlib into a git submodule

[Christian König]

Am 09.08.2016 um 15:47 schrieb Nicolai Hähnle:
> Hi everybody,
>
> addrlib is the addressing and alignment calculator which is used by 
> radeonsi. It's developed (and also used) internally at AMD, and so far 
> we've had one open source copy living in the Mesa repository at 
> src/gallium/winsys/amdgpu/drm/addrlib.
>
> The question of using addrlib in non-Mesa parts of our open-source 
> stack has come up, in particular in relation to compute. We'd 
> obviously like to share the code rather than having multiple copies 
> flying around. Since the interface of addrlib is slow-moving but 
> unstable, shared linking is not an option.
>
> I think the best way forward is to create a dedicated repository for 
> addrlib which is then integrated into Mesa as a git submodule.
>
> The point of this email is to gather feedback from the Mesa community 
> on this plan, which is explicitly:
>
> (0) Create an addrlib repository, say amd/addrlib on fd.o.
> (1) Add it as a git submodule to the Mesa repository.
> (2) Fix up whatever aspects of the build system that may be affected 
> (perhaps for building source tarballs).
> (3) Go back to mostly ignoring addrlib, except for trying to get 
> better at syncing with the internal closed-source version.
>
> From initial experiments, the impact on users interested in radeon is 
> that they will have to run `git submodule init` and then occasionally 
> `git submodule update`. Users who do not build radeonsi should be able 
> to ignore the change completely.
>
> There are alternatives. For example, ROCm uses Google's repo tool 
> already. But for Mesa, git submodule looks like a lightweight, well 
> supported and overall conservative option that everybody should 
> already have installed. If there are good arguments for something 
> else, let's hear them!
>
> Another point: if we proceed with this plan, I think we should 
> consider moving addrlib into src/amd/addrlib. There are two reasons: 
> First, transitioning to a submodule *without* changing the directory 
> is probably more fragile, i.e. what happens when you switch between 
> checkouts before and after the transition. Second, if/when radv ends 
> up being merged into Mesa master, it makes sense to have addrlib there 
> anyway.
>
> Thoughts? Complaints? Praise?

Well using git submodule is a possibility and we had rather good 
experience with that in GStreamer.

But it would remove one major argument to beating the addrlib guys 
towards a stable interface and/or proper library version handling.

Moving it into libdrm is clearly not an option because then you would 
need to use versioning for the whole libdrm_amdgpu library which we 
don't want.

Christian.

> Nicolai
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